Posers and Puzzles
04 Dec 06
04 Dec 06
Originally posted by dmnelson84Yes, I'm skeptical by nature. Sorry, but the thought of that poor sap drawing nine lines for every 'nine', and then counting all the myriad intersections, and then doing all the 'carrying' just struck me as funny.
BigDogg, has anyone ever told you that you're a bit of a downer? So many of your posts are condescending.
04 Dec 06
Originally posted by dmnelson84I've got a pretty neat trick for doing multiplication in your head. Successive approximation.
In your case, skeptical is just a euphemism for rude.
To take the example in the video: 21 x 13.
10 * 2 * 13 = 260
+
1*13
=
273
And a harder example: 54 x 37
50 * 40 = 2000
-
50 * 3
1850
4 * 40 = 160
-
4 * 3
148
1850 + 148 = 1998
Why would you need more tricks than this?
04 Dec 06
1 edit
I disagree with most of the remarks made above. The principle is very good, and can be applied without doing the graphics (and regardless the number of 9's). Only, you have to do the exercise from right to left, so you can write down the solution from right to left character by character without overloading your memory. In real-life exercises, once the person has acquired the skill, multpilications of 5x5 numbers can be done 10+ times faster by the same person than with any other manual method.
04 Dec 06
Originally posted by zebanoUsing marbles, I can represent 3*2 as 3 groups of two marbles each. The trick on the video simply substitutes line intersections for marbles. The lines are all drawn diagonally to keep the proper order of magnitude for each number.
Neat trick, totally impractical. I just wonder how many people can prove why it works*.
😵
*should be trivial if you know how multiplication works (I too am a skeptic).
However, try the intersection trick for 9*9, and you will see why we use times tables instead.